Re: [PATCH 4/4] perf python: Add counting.py as example for counting perf events

[Ian Rogers]

On Thu, May 1, 2025 at 2:37 AM Gautam Menghani <gautam@xxxxxxxxxxxxx> wrote:
>
> Add counting.py - a python version of counting.c to demonstrate
> measuring and reading of counts for given perf events.
>
> Signed-off-by: Gautam Menghani <gautam@xxxxxxxxxxxxx>
> ---
>  tools/perf/python/counting.py | 41 +++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
>  create mode 100755 tools/perf/python/counting.py
>
> diff --git a/tools/perf/python/counting.py b/tools/perf/python/counting.py
> new file mode 100755
> index 000000000000..0c58907bd8bf
> --- /dev/null
> +++ b/tools/perf/python/counting.py
> @@ -0,0 +1,41 @@
> +#!/usr/bin/env python3
> +# SPDX-License-Identifier: GPL-2.0
> +# -*- python -*-
> +# -*- coding: utf-8 -*-
> +
> +import perf
> +
> +def main():
> +        cpus = perf.cpu_map()
> +        thread_map = perf.thread_map(-1)
> +        evlist = perf.evlist(cpus, thread_map)
> +
> +        evsel1 = perf.evsel(type = perf.TYPE_SOFTWARE,
> +                 config = perf.COUNT_SW_CPU_CLOCK,
> +                 read_format = perf.FORMAT_TOTAL_TIME_ENABLED | perf.FORMAT_TOTAL_TIME_RUNNING,
> +                 disabled=1)
> +        evlist.add(evsel1)
> +
> +        evsel2 = perf.evsel(type = perf.TYPE_SOFTWARE,
> +                 config = perf.COUNT_SW_TASK_CLOCK,
> +                 read_format = perf.FORMAT_TOTAL_TIME_ENABLED | perf.FORMAT_TOTAL_TIME_RUNNING,
> +                 disabled=1)
> +        evlist.add(evsel2)

Nice example! Would this be better as:
```
    cpus    = perf.cpu_map()
    threads = perf.thread_map(-1)
    evlist = perf.parse_events("cpu-clock,task-clock", cpus, threads)
```
If you run `perf stat -vv -e 'cpu-clock,task-clock' .. ` you can
double check the perf event attribute bits. For example in
tracepoint.py we remove the SAMPLE_IP:
https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/python/tracepoint.py?h=perf-tools-next#n27

> +
> +        evlist.open()
> +        evlist.enable()
> +
> +        count = 100000
> +        while count > 0:
> +            count -= 1
> +
> +        evlist.disable()
> +        evsel = evlist.next(None)
> +        while evsel != None:
> +            counts = evsel.read(0, 0)

Rather than just reading on the first CPU and thread, perhaps change
to iterate over the cpus and threads? Something like:
```
    for evsel in evlist:
        for cpu in cpus:
            for thread in threads:
                counts = evsel.read(cpu, thread)
                print(f"For {evsel} read val={counts.val}
enable={counts.ena} run ={counts.run}")
```

Thanks,
Ian

> +            print(counts.val, counts.ena, counts.run)
> +            evsel = evlist.next(evsel)
> +        evlist.close()
> +
> +if __name__ == '__main__':
> +    main()
> --
> 2.49.0
>